US3508651A - Method and apparatus for screening pulp - Google Patents

Description

A ril 28, 1970 I s. w. H. HOOPER 3,503,651-

METHOD AND APPARATUS FOR SCREENING PULP Filed April 19, 1968 3 Sheets-Sheet l c0 (\J CD 8 l N U- INVENTOR. SM. H. HOOPER April 28, 1970 s. w. H. HOOPER METHOD AND APPARATUS FOR SCREENING PULP 3 Sheets-Sheet 2 Filed April 19, 1968 INVENTOR. 5. MH. HOOPER %J;fwf 9 April 8, 1970 s. w. H. HOOPER 3,508,651

METHOD AND APPARATUS FOR SCREENING PULP Filed April 19, 1968 3 Sheets-Sheet 3 FIG. 5 32 33 26 INVENIOR. I 5. W. H. HOOPER BY WM 6.

United States Patent 3,508,651 METHOD AND APPARATUS FOR SCREENING PULP Sydney W. H. Hooper, Sherbrooke, Quebec, Canada, as-

signor to S. W. Hooper & Co., Ltd., Sherbrooke,

Quebec. Canada Filed Apr. 19, 1968, Ser. No. 730,672 Int. Cl. B01d 29/42, 35/16, 35/22 US. Cl. 210-65 18 Claims ABSTRACT OF THE DISCLOSURE A pulp screen of the horizontal pressure type having a cylindrical screen and an impeller mounted for rotation within the screen, a conical core on the impeller shaft defines a primary compartment adjacent the pulp stock inlet and a secondary compartment remote from the stock inlet, a series of blades radiate from the impeller shaft and define a series of radial passages extending the length of the conical core, a section of the impeller shaft remote from the stock inlet of the machine conducts dilution water to a series of apertures in the shaft and to the radial passages and into an annular passage formed at the base of the conical core, and a series of nozzles on the side of the base of the conical core within the secondary compartment are connected with the annular passage to receive dilution water therefrom and project the dilution water radially towards the adjacent portion of the cylindrical screen.

The present invention relates to the rotary screening of pulp stock and more particularly to the horizontal pressure type of pulp screening to separate acceptable fibres from reject material.

In the conventional pressure or drowned type of pulp screening apparatus the acceptable fibres of the pulp stock introduced into the apparatus are passed through the screen while the reject material is moved through the screen chamber to a discharge outlet. To accomplish this an impeller is mounted axially in a horizontal cylindrical screen to move the pulp to the periphery of the screen chamber. In order to dilute the stock and assist in washing the fibres through the screen an impeller has been developed with radiating passages for carrying dilution liquid towards the screen. Such apparatus suffers from the disadvantage that the reject material does not readily move along the periphery of the screen chamber towards the discharge outlet and tends to clog the screen. In another type of impeller there is provided a conical core mounted on the impeller shaft with its base defining a secondary compartment remote from the pulp stock inlet. The conical core presents progressively decreasing annular area of flow within the screen chamber which speeds up the stock flow in the direction of the secondary compartment. The secondary compartment receives dilution liquid and the pulp stock is further washed to reclaim any remaining acceptable fibres which would otherwise. be discharged with the reject material. This type of apparatus had the disadvantage that no dilution liquid is introduced into the primary compartment of the screen chamber. Also, the dilution liquid introduced into the secondary compartment is not efficiently employed to reach the outer periphery of that compartment at the screen.

It is an object of the present invention to provide a method and apparatus for horizontal pressure type pulp screening using a cylindrical screen and an impeller with a conical core, in which dilution water is introduced into both the primary and secondary compartments of the screen chamber formed by the base of the core to improve the separation of the acceptable fibres in the pulp stock "ice from the reject material and thereby increase the efiiciency of the operation.

In its broadest aspect the invention consists of a method of screening pulp in a horizontal pressure type screening device having a rotatable impeller axially aligned within a closed cylindrical screen, the impeller having a conical core with the base thereof dividing the screen chamber of the screen into a primary compartment and a secondary compartment interconnected about the periphery of the base of the core with the primary compartment, comprising the steps of: (a) introducing pulp stock under pressure into the primary compartment of the screen chamber axially of the impeller and remote from the secondary compartment; (b) introducing dilution liquid under pressure into the primary compartment of the screen chamber radially of the impeller axis and channelling said liquid towards the screen; (c) introducing dilution liquid under pressure into the secondary compartment of the screen chamber; (d) rotating the impeller to direct the pulp stock towards the screen for passage of acceptable pulp fibre material therethrough; (e) collecting the accessible pulp fibres after passage through the screen; and (f) discharging reject material from the secondary compartment. Preferably the dilution liquid is introduced into the primary compartment only in the region of the core and at least a portion of the dilution liquid is introduced into the secondary compartment adjacent the periphery of the base of the core and in the direction of the screen.

Another aspect of the invention resides in a rotary pulp screening apparatus having a horizontal cylindrical closed screen and a rotary impeller axially mounted therein, comprising: (a) a pulp stock inlet opening into the chamber of the screen axially co-extensive therewith and with the impeller; (b) a conical core fixed on the impeller with the base thereof defining a primary compartment adjacent the inlet and a secondary compartment remote from the inlet and interconnected with the primary compartment at the periphery of the base of the core; (0) means to introduce dilution liquid under pressure into the primary compartment radially of the impeller axis and to channel said liquid towards the screen; (d) means to introduce dilution liquid under pressure into the secondary compartment; (e) means to collect acceptable pulp fibres after passage through the screen; (f) outlet means to remove the reject material from the secondary compartment; and (g) means externally to connect the impeller with driving means. In a preferred embodiment radial apertures are provided in the shaft of the impeller opening into radial slots in the core extending its length to channel dilution liquid, introduced into the primary compartment of the screen chamber through the apertures, towards the screen. In the secondary compartment the means to introduce dilution liquid preferably includes a plurality of nozzles projecting laterally from the base of the conical core adjacent its periphery and having the outlets of the nozzles directed towards the screen.

An example embodiment of the invention is shown in the accompanying drawings in which:

FIGURE 1 is a cross-sectional view in elevation of a pulp screening device according to the invention;

FIGURE 2 is a cross-sectional view in elevation showing the impeller of the pulp screening device of FIG- URE 1;

FIGURE 3 is a cross-section taken along the line 33 of FIGURE 2;

FIGURE 4 is a cross-section taken along the line 44 of FIGURE 2;

FIGURE 5 is a fragmentary view of the impeller taken along the line 55 of FIGURE 2;

FIGURE 6 is a view taken along the line. 6-6 of FIGURE 5; and

FIGURE 7 is a cross-sectional view taken along the line 77 of FIGURE 2.

In the drawings FIGURE 1 shows a horizontal pressure-type pulp screening device consisting of a casing or housing 10 having a cylindrical wall 11, a forward end wall 12 and a rearward end wall 13. A horizontal cylindrical screen 14 is mounted concentrically with rotor shaft 43 and is closed by end walls 12 and 13 to form a. screen chamber 15. Housing 10 includes a main discharge outlet 16 located in the lower portion of cylindrical wall 11.

A pulp stock inlet pipe 17 leads into screen chamber through an opening 18 in forward end wall 12 of frame 10, opening 18 being in coaxial alignment with screen 14. A rotor or impeller 19 is located in screen chamber 15 and has a shaft 20 coaxial with screen 14 and opening 18. One end of shaft 20 is journally mounted in a bearing support 21 fixed to inlet pipe 17 and the other end of the shaft is journally mounted in a bearing housing 22 fixed on the outside of rearward end wall 13 of housing 10. Packings 23 circumscribing shaft 20 provide watertight seals for bearings 21 and 22. A sheave 24 is fixed to shaft 20 outside bearing housing 22 while the shaft at its free end meets an inlet coupling 25.

As shown more particularly in FIGURES 2, 3 and 4 of the drawings, impeller 19 consists of a plurality of equally spaced fixed radial primary blades 26 having their outer or peripheral edges 26a located adjacent screen 14. The forward or leading edge 26b of blade 26 is located adjacent forward end wall 12 and has an undercut 27. An end ring 28 fixed to blades 26 holds them in spaced relationship at their leading edges 26b while their rearward or trailing edges 26c are fixed to a transverse circular baflie 29 which is fixed on shaft 20 in spaced relationship with rearward end wall 13 of housing 10 to divide screen chamber 15 into a primary compartment 30 and a secondary compartment 31.

A plurality of secondary blades 32 are fixed to shaft 20, one blade 32 being parallel to each primary blade 26 to form therewith a passage 33 substantially in an axial plane of shaft 20 and extending radially outwardly towards screen 14. The rearward or trailing edges 320 of blades 32 are fixed to transverse bafile 29 and the blades extend forwardly approximately three-fifths the length of blades 26. Blades 32 are fixed at their forward or leading edges 3212 by an intermediate ring 34.

A conical core member 35 is located on shaft 20 in the region of blades 32 and is formed by a plurality of triangular plates or spacers 36 fixed on the side of each primary blade 26 opposite passage 33 between that blade and the next circumferentially positioned secondary blade 32. Each plate 36 extends from shaft 20 adjacent the leading edges 32b of blades 32 outwardly and rearwardly to meet bafiie 29 adjacent the outer edges 32a of those blades. From FIGURE 3 it will be. seen that conical core 35 is traversed by passages 33, the passages forming substantially radial slots in the core extending its length.

The outer edge portion of each of blades 26 and 32 extends rearwardly of bafile 29 to form a plurality of double-walled vanes 37 projecting into secondary compartment 31 and located around the periphery of the bafiie. The double walls of each vane 37 act as the sidewalls of a nozzle 38 with a supporting bracket 39 and an end plate 40 acting as two further walls and a bottom plate 41 with apertures 42 acting as the nozzle outlet which is directed against screen 14.

Shaft 20 of impeller 19 consists of a solid portion 43 located forwardly of blades 32 and a tubular portion 44 throughout the remainder of the shaft. As seen more particularly in FIGURE 2 of the drawings, the wall of tubular portion 44 of shaft 20 has a series of longitudinal rows of apertures 45, each row of apertures opening into a passage 33 between blades 26 and 32 in the region of core 35. A pipe 46 mounted concentrically Within tubular portion 44 of shaft 20 connects an inlet 47 of coupling 25 with apertures 45 and provides an annular passage 48 leading from a second inlet 50 in coupling 25, the end of passage 48 being sealed with an O-ring 49. The end of passage 48 adjacent sealing ring 49 connects through an aperture 51 with a passage 52 lying against bafiie 29 at the end of each passage 33. Passage 52 leads through an aperture 53 in the baffie into nozzle 38.

The rearward tubular end of shaft 20 terminates in a stationary bearing 54 fixed to inlet coupling 25 and pipe 46 extends rearwardly beyond the end of shaft 20 to terminate at inlet 47 of the coupling. Fixed spacers 55, together with sealing ring 49 maintain pipe 46 concentrically positioned within shaft 20. A friction ring 56 located between the rearward end of shaft 20 and stationary bearing 54 while a friction ring 57 is located between the end of pipe 46 and stationary coupling 22.

A further inlet conduit 58 opens through rearward end wall 13 of housing 10 into secondary compartment 31 of screen chamber 15 while an outlet 59 opens from a lower portion of compartment 31 through end wall 13.

In the operation of the invention impeller 19 is driven through sheave 24 by pulley drive means not shown. Pulp stock, consisting of acceptable pulp fibres and reject material, is pumped under pressure through inlet pipe 17 into screen chamber 15 While dilution liquid, usually white water from the pulp mill, is pumped under pressure both through inlets 47 and 50 of coupling 25 and through inlet 58 into screen chamber 15. Undercuts 27 of blades 26 allow unobstructed flow of the pulp stock into screen chamber 15 from inlet pipe 17 and this stock is directed towards screen 14 by the rotation of impeller 19 as it flows axially between blades 26 (and blades 32). That portion of the pulp stock flowing into passages 33 is assisted in its redirection towards screen 14 by the dilution liquid flowing from inlet 47 through pipe 46 and the tubular portion 44 of shaft 20 to emanate from apertures 45. This dilution liquid is channelled towards screen 14 by passages 33 and, when it reaches the outer edges 26a of blades 26, washes the pulp stock and assists in the passage of acceptable pulp fibres through the screen for withdrawal from housing 10 through outlet 16.

As the acceptable pulp fibres are passed through screen 14 it is necessary to remove the rejected material of the pulp stock in order to prevent blockage of the screen and to provide continuity in the operation of the apparatus. Conical core 35 provides a progressively decreasing annular cross-section of fiow in primary compartment 30 of screen chamber 15 in the direction of end wall 13 and this progressive restriction causes the flow of pulp stock to speed up as it moves longitudinally through the screen chamber, thus accelerating the removal of reject material from the vicinity of screen 14. This reject material, together with a residual amount of acceptable pulp fibres, passes over baffle 29 into secondary compartment 31 of screen chamber 15 where is it immediately subjected to further dilution liquid flow from nozzles 38 causing separation and reclamation of acceptable pulp fibres which were not separated in primary compartment 30. As the reject material continues to pass into secondary compartment 31 it is again mixed with dilution liquid entering the compartment from inlet 58. This mixture is stirred by vanes 37 which drive substantially all the remaining acceptable pulp fibres through screen 14. The reject material, throughly washed in this manner by the dilution liquid in secondary compartment 31, is drawn continuously from secondary compartment 31 through outlet 59 to effect continuous flow of the pulp stock through the apparatus.

The present invention is effective in separating and recovering substantially all the acceptable fibres present in the pulp stock delivered to the screening device and this is accomplished in an efficient manner. The introduction of dilution liquid (usually white water from pulp mill) into primary compartment 30 of screen chamber 15 allows the pulp material to be gently washed adjacent screen 14 by the action of blades 26 of impeller 19 and in this manner the maximum amount of acceptable fibre material is separated. The presence of core 35 causes the reject material to move into secondary compartment 31 where the introduction of further dilution liquid out in the area of the primary compartment thoroughly washes out substantially all the remaining acceptable fibres which are then passed through screen 14 by the action of vanes 37. The preferential use of nozzles 38 further facilitates separation of the acceptable fibres from the reject material by mixing dilution liquid with the pulp stock immediately as it passes baflle 29 from primary compartment 15 to secondary compartment 31. By impinging the dilution liquid from nozzles 38 onto screen 14 the pulp stock entering he secondary compartment is again gently washed and the acceptable fibres are directed through the screen.

I claim:

1. A method of screening pulp in a horizontal pres sure type screening device having a rotatable impeller axially aligned within a closed cylindrical screen, the impeller having a series of blades, a conical core with the base thereof dividing the screen chamber of the screen into a primary compartment and a secondary compartment interconnected about the periphery of the base of the core with the primary compartment, the said core having a series of plates extending from the surface thereof and spaced parallel to said blades, comprising the steps of: (a) introducing pulp stock under pressure into the primary compartment of the screen chamber between the blades of the impeller and said plates axially of the impeller and remote from the secondary compartment; (b) introducing dilution liquid under pressure into the primary compartment of the screen chamber radially of the impeller axis and channelling said liquid towards the screen; (c) introducing dilution liquid under pressure into the secondary compartment of the screen chamber; (d) rotating the impeller to direct the pulp stock towards the screen for passage of acceptable pulp fibre material therethrough; (e) collecting the acceptable pulp fibres after passage through the screen; and (f) discharging reject material from the secondary compartment.

2. A method as claimed in claim 1 in which the dilution liquid is introduced into the primary compartment only in the region of the core.

3. A method as claimed in claim 1 in which at least a portion of the dilution liquid is introduced into the secondary compartment adjacent the periphery of the base of the core and in the direction of the screen.

4. A rotary pulp screening apparatus having a horizontal cylindrical closed screen and a rotary impeller axially mounted therein, comprising: (a) a pulp stock inlet opening into the chamber of the screen axially coextensive therewith and with the impeller; (b) a conical core fixed on the impeller with the base thereof defining a primary compartment adjacent the inlet and a secondary compartment remote from the inlet and inter-connected with the primary compartment at the periphery of the base of the core and a series of plates extending from the surface of the core and spaced parallel to the blades of the impeller; (c) means to introduce dilution liquid under pressure into the primary compartment radially of the impeller axis and to channel said liquid towards the screen through the space between the blades of the impeller and the said plates; (d) means to introduce dilution liquid under pressure into the secondary compartment; (e) means to collect acceptable pulp fibres after passage through the screen; (f) outlet means to remove the reject material from the secondary compartment; and (g) means externally to connect the impeller with driving means.

5. An apparatus as claimed in claim 4 in which the dilution liquid is introduced into the primary compartment through radial apertures in the shaft of the impeller and through radial slots in the core extending the length thereof.

6. An apparatus as claimed in claim, 4 in which the means to introduce dilution liquid into the secondary compartment of the screen chamber includes a plurality of nozzles projecting laterally from the base of the core adjacent the periphery thereof and having the outlets thereof directed towards the screen.

7. An apparatus as claimed in claim 4 in which the base of the conical core comprises a battle.

8. An apparatus as claimed in claim 5 in which pairs of spaced parallel blades of the impeller extend the passages formed by said slots radially towards the screen.

9. A rotary pulp pressure type horizontal screening apparatus comprising: a closed cylindrical screen; a rotatable impeller mounted co-axially within the chamber formed by the screen; a conical core fixed coaxially on the impeller between the blades thereof, said core enlarging rearwardly from the inlet with the base thereof dividing the chamber into a primary compartment and a secondary compartment interconnected at the periphery of the base with the primary compartment, a series of plates extending from the surface of the core and spaced parallel to the blades of the impeller, means to introduce dilution liquid into the spaces between the blades and said plates, a pulp stock inlet opening into the primary compartment of the screen chamber coaxially with the impeller; a plurality of radial slots in the core extending the length thereof; means to introduce dilution liquid under pressure through the impeller shaft into the slots and to channel said liquid to the peripheral edges of the blades of the impeller; "means to introduce dilution liquid under pressure into the secondary compartment; means on the impeller to mix dilution liquid introduced into the secondary compartment with pulp stock entering therein from the primary compartment; means to collect the acceptable fibres passing through the screen and to remove the reject material of the pulp stock from the secondary compartment; and means externally to connect the impeller with driving means whereby the impeller is rotated.

10. An apparatus as claimed in claim 9 in which the impeller shaft is tubular with radial apertures therein connecting with the slots in the conical core, and means to deliver dilution liquid into the shaft.

11. An apparatus as claimed in claim 9 in which the mixing means comprises vanes extending from the base of the core into the secondary compartment.

12. An apparatus as claimed in claim 11 in which the means to introduce dilution liquid into the secondary compartment includes a plurality of nozzles mounted on the periphery of the base of the core and extending into the secondary compartment, the outlet of the nozzles being directed towards the screen.

13. An apparatus as claimed in claim 12 in which the impeller shaft is tubular and radially connected with the nozzles through conduits located in the slots of the core, and means to deliver dilution liquid into the shaft.

14. In a rotary pressure type horizontal pulp screening apparatus having a pulp stock inlet at one closed end of a cylindrical screen and a reject outlet at the other end thereof; an impeller rotatably mounted within the screen coaxially therewith and with the inlet, a plurality of primary blades extending radially from the shaft of the impeller, a plurality of secondary blades extending radially from the shaft of the impeller in parallel with the primary blades and forming passages therewith substantially in the plane of the shaft axis, the ends of the primary and secondary blades remote from the inlet terminating in a baffle fixed transversely to the impeller shaft and spaced from the reject outlet to form a secondary compartment therewith, spacers mounted between said blades to form a conical core radially slotted by said passages with the baffle forming the base of the core, means to introduce dilution liquid, under pressure into the secondary compartment, and means to introduce dilution liquid under pressure radially from the impeller shaft into the passages formed by the primary and secondary blades and in the direction of the screen.

15. An apparatus as claimed in claim 14 in which the leading edges of the primary blades terminate adjacent the inlet end of the screen and the leading edges of the secondary blades are spaced from said inlet end, the conical core extending substantially from the leading edges of the secondary blades to the bafile.

16. An apparatus as claimed in claim 14 in which the outer edge portions of the primary and secondary blades extend rearwardly of the baffle into the secondary compartment to provide vanes therein spaced about the periphery of the baffie.

17. An apparatus as claimed in claim 16 in which the means to introduce dilution liquid into the secondary compartment include nozzle means located between the walls of each said vane, the outlet of said nozzle means being directed toyi ards the screen.

18. An apparatus as claimed in claim .17 in which the impeller shaft carries an internal pipe defining a central passage and an annular passage, the central passage being connected with the apertures opening into the passages formed by the primary and secondary blades and the annular passage being connected with the nozzle, and means to introduce dilution liquid separately into said passages.

References Cited UNITED STATES PATENTS 3,081,873 3/1963 Cowan et a1. 209380 X 3,243,041 3/1966 Cowan 209-273 3,245,535 4/1966 Cowan 209-306 X J. L. DECESARE, Primary Examiner US. Cl. X.R.

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